Method of transmitting feedback data in a multiple antenna system

ABSTRACT

A method of transmitting feedback data in a multiple antenna system comprises receiving a request message of feedback data on a downlink channel, the request message comprising uplink scheduling information, selecting a set of M (M≧1) subbands within a plurality of subbands, generating the feedback data, the feedback data comprising a frequency selective PMI (preceding matrix indicator), a frequency flat PMI, a best band CQI (channel quality indicator) and a whole band CQI, and transmitting the feedback data on a uplink channel allocated to the uplink scheduling information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisionalapplication Ser. No. 60/978,140 filed on Oct. 8, 2007, U.S. Provisionalapplication Ser. No. 61/025,304 filed on Feb. 1, 2008, Korean PatentApplication No. 10-2007-0080519 filed on Aug. 10, 2007, Korean PatentApplication No. 10-2007-0081913 filed on Aug. 14, 2007, Korean PatentApplication No. 10-2007-0118168 filed on Nov. 19, 2007, Korean PatentApplication No. 10-2008-0005864 filed on Jan. 18, 2008, and KoreanPatent Application No. 10-2008-0073340 filed on Jul. 28, 2008 which areincorporated by reference in its entirety herein.

BACKGROUND

1. Technical Field

The present invention relates to wireless communications, and moreparticularly, to a method for transmitting feedback data in a multipleantenna system.

2. Related Art

Wireless communication systems are widely used to provide various typesof communications. For example, voice and/or data are provided by thewireless communication systems. A conventional wireless communicationsystem provides multiple users with one or more shared resources. Forexample, the wireless communication system can use various multipleaccess schemes such as code division multiple access (CDMA), timedivision multiple access (TDMA), and frequency division multiple access(FDMA).

An orthogonal frequency division multiplexing (OFDM) scheme uses aplurality of orthogonal subcarriers. Further, the OFDM scheme uses anorthogonality between inverse fast Fourier transform (IFFT) and fastFourier transform (FFT). A transmitter transmits data by performingIFFT. A receiver restores original data by performing FFT on a receivedsignal. The transmitter uses IFFT to combine the plurality ofsubcarriers, and the receiver uses FFT to split the plurality ofsubcarriers. According to the OFDM scheme, complexity of the receivercan be reduced in a frequency selective fading environment of abroadband channel, and spectral efficiency can be improved throughselective scheduling in a frequency domain by utilizing channelcharacteristics which are different from one subcarrier to another. Anorthogonal frequency division multiple access (OFDMA) scheme is anOFDM-based multiple access scheme. According to the OFDMA scheme, aradio resource can be more efficiently used by allocating differentsubcarriers to multiple users.

Recently, to maximize performance and communication capability of thewireless communication system, attention is paid to a multiple inputmultiple output (MIMO) system. Being evolved from the conventionaltechnique in which a single transmit (Tx) antenna and a single receive(Rx) antenna are used, a MIMO technique uses multiple Tx antennas andmultiple Rx antennas in order to improve efficiency of data transmissionand reception. The MIMO system is also referred to as a multiple antennasystem. In the MIMO technique, instead of receiving one whole messagethrough a single antenna path, data segments are received through aplurality of antennas and are then assembled into one piece of data. Asa result, a data transfer rate can be improved in a specific range, or asystem range can increase with respect to a specific data transfer rate.

Hereinafter, downlink is defined as a communication link from a basestation (BS) to a user equipment (UE), and uplink is defined as acommunication link from the UE to the BS.

In general, the BS schedules uplink and downlink radio resources in thewireless communication system. User data or control signals are carriedusing the uplink and downlink radio resources. A channel for carryinguser data is referred to as a data channel. A channel for carryingcontrol information is referred to as a control channel.

For radio resource scheduling of the BS, the UE reports feedback data tothe BS. In the multiple antenna system, the feedback data includes achannel quality indicator (CQI), a rank indicator (RI), a precedingmatrix indicator (PMI), etc. The UE transmits the feedback data (e.g.,CQI, RI, PMI, etc.) to the BS. According to the feedback data receivedfrom a plurality of UEs, the BS schedules uplink and downlink radioresources. A whole frequency band is divided into a plurality ofsubbands. The BS can schedule the radio resources for each subband. Froman aspect of radio resource scheduling of the BS, it is most effectivewhen the UE obtains respective CQIs and PMIs for all subbands andreports the obtained CQIs and PMIs to the BS. However, a significantlylarge overhead is caused when the CQIs and PMIs for all subbands aretransmitted with limited radio resources.

Accordingly, there is a need for a method for effectively transmittingCQIs and PMIs in a multiple antenna system.

SUMMARY

The present invention provides a method for transmitting feedback datain a multiple antenna system.

In an aspect, a method of transmitting feedback data in a multipleantenna system comprises receiving a request message of feedback data ona downlink channel, the request message comprising uplink schedulinginformation, selecting a set of M (M≧1) subbands within a plurality ofsubbands, generating the feedback data, the feedback data comprising afrequency selective PMI (preceding matrix indicator), a frequency flatPMI, a best band CQI (channel quality indicator) and a whole band CQI,the frequency selective PMI indicating the index of a preceding matrixselected from a codebook over the M selected subbands, the frequencyflat PMI indicating the index of a preceding matrix selected from thecodebook over the plurality of subbands, the best band CQI indicating aCQI value over the M selected subbands, the whole band CQI indicating aCQI value over the plurality of subbands, and transmitting the feedbackdata on a uplink channel allocated to the uplink scheduling information.

In another aspect, a method of transmitting feedback data in a multipleantenna system comprises selecting a set of M (M≧1) subbands within aplurality of subbands, and transmitting feedback data on a uplink sharedchannel, the feedback data comprising a frequency selective PMI, afrequency flat PMI, a best band CQI and a whole band CQI, the frequencyselective PMI indicating the index of a preceding matrix selected from acodebook over the M selected subbands, the frequency flat PMI indicatingthe index of a preceding matrix selected from the codebook over theplurality of subbands, the best band CQI indicating a CQI value over theM selected subbands, the whole band CQI indicating a CQI value over theplurality of subbands.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 is a block diagram showing a transmitter having multipleantennas.

FIG. 3 is a block diagram showing a receiver having multiple antennas.

FIG. 4 shows an example of a granularity of a radio resource accordingto an embodiment of the present invention.

FIG. 5 shows an example of transmitting a channel quality indicator(CQI) and a preceding matrix indicator (PMI).

FIG. 6 shows another example of transmitting a CQI and a PMI.

FIG. 7 shows another example of transmitting a CQI and a PMI.

FIG. 8 shows a method for generating feedback data according to anembodiment of the present invention.

FIG. 9 shows a method for generating feedback data according to anotherembodiment of the present invention.

FIG. 10 shows a method for transmitting feedback data according to anembodiment of the present invention.

FIG. 11 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 12 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 13 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 14 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 15 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 16 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 17 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 18 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 19 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 20 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 21 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 22 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 23 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 24 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 25 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 26 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 27 shows a method for transmitting feedback data according toanother embodiment of the present invention.

FIG. 28 is a graph showing an example of a data efficiency ratio when anuplink PMI is transmitted.

FIG. 29 is a graph showing another example of a data efficiency ratiowhen an uplink PMI is transmitted.

FIG. 30 is a flowchart showing a method for generating feedback dataaccording to an embodiment of the present invention.

FIG. 31 is a flowchart showing a method for selecting a PMI by detectingan error from feedback data according to an embodiment of the presentinvention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a wireless communication system. The wireless communicationsystem can be widely deployed to provide a variety of communicationservices, such as voices, packet data, etc.

Referring to FIG. 1, the wireless communication system includes at leastone user equipment (UE) 10 and a base station (BS) 20. The UE 10 may befixed or mobile, and may be referred to as another terminology, such asa mobile station (MS), a user terminal (UT), a subscriber station (SS),a wireless device, etc. The BS 20 is generally a fixed station thatcommunicates with the UE 10 and may be referred to as anotherterminology, such as a node-B, a base transceiver system (BTS), anaccess point, etc. There are one or more cells within the coverage ofthe BS 20.

There is no restriction on a multiple access scheme used in the wirelesscommunication system. The multiple access scheme may be based on codedivision multiple access (CDMA), time division multiple access (TDMA),frequency division multiple access (FDMA), single-carrier FDMA(SC-FDMA), orthogonal frequency division multiple access (OFDMA), orother well-known modulation schemes. For clarity, an OFDMA-basedwireless communication system will be described hereinafter.

The wireless communication system may be a multiple antenna system. Themultiple antenna system may be a multiple input multiple output (MIMO)system. Alternatively, the multiple antenna system may be amultiple-input single-output (MISO) system or a single-inputmultiple-output (SIMO) system. The MIMO system uses a plurality oftransmit (Tx) antennas and a plurality of receive (Rx) antennas. TheMISO system uses a plurality of Tx antennas and one Rx antenna. The SIMOsystem uses one Tx antenna and a plurality of Rx antennas.

FIG. 2 is a block diagram showing a transmitter having multipleantennas.

Referring to FIG. 2, a transmitter 100 includes a scheduler 110, channelencoders 120-1 to 120-K, mappers 130-1 to 130-K, precoders 140-1 to140-K, and a multiplexer 150. The transmitter 100 includes Nt (Nt>1) Txantennas 190-1 to 190-Nt. The transmitter 100 may be a part of a BS indownlink. The transmitter 100 may be a part of a UE in uplink.

The scheduler 110 receives data from N users and outputs K streams to beconcurrently transmitted. By using channel information of each user, thescheduler 110 determines a user and a data transfer rate fortransmitting data through available radio resources. The scheduler 110extracts a CQI from feedback data, and selects a modulation and codingscheme (MCS) or the like. The CQI includes a signal to noise ratio(SNR), a signal to interference and noise ratio (SINR), etc., determinedbetween the transmitter and a receiver.

The available radio resources allocated by the scheduler 110 denoteradio resources used for data transmission in the wireless communicationsystem. For example, all time slots are resources in a TDMA system, allcodes and time slots are resources in a CDMA system, and all subcarrierand time slots are resources in an OFDMA system. The respectiveresources may be orthogonal to each other by definition in a time, code,or frequency domain so that interference to another user does not occurin the same cell or sector.

The channel encoders 120-1 to 120-K encode input streams according to apredetermined coding scheme, and thus generate coded data. The mappers130-1 to 130-K map the coded data onto symbols representing locations ona signal constellation. These symbols are called data symbols. There isno restriction on a modulation scheme. The modulation scheme may bem-phase shift keying (m-PSK) or m-quadrature amplitude modulation(m-QAM). For example, the m-PSK may be binary PSK (BPSK), quadrature PSK(QPSK), or 8-PSK. The m-QAM may be 16-QAM, 64-QAM, or 256-QAM.

The precoders 140-1 to 140-K perform preceding on received data symbolsu₁, . . . , u_(K) and thus generate input symbols x₁, . . . , x_(K). Thepreceding is a scheme for pre-processing data symbols to be transmitted.Examples of the preceding scheme include random beamforming (RBF), zeroforcing beamforming (ZFBF), etc., in which input symbols are generatedby applying a weighting vector or a preceding matrix to the datasymbols.

The multiplexer 150 assigns the input symbols x₁, . . . , x_(K) tosuitable subcarriers, and multiplexes the symbols according to a user.The multiplexed symbols are modulated and then transmitted through theTx antennas 190-1 to 190-Nt.

FIG. 3 is a block diagram showing a receiver having multiple antennas.

Referring to FIG. 3, a receiver 200 includes a demodulator 210, achannel estimator 220, a post-coder 230, a demapper 240, a channeldecoder 250, and a controller 260. Further, the receiver 200 includes Nr(Nr>1) Rx antennas 290-1 to 290-Nr. The receiver 200 may be a part of aUE in downlink. The receiver 200 may be a part of a BS in uplink.

Signals received from the Rx antennas 290-1 to 290-Nr are demodulated bythe demodulator 210. The channel estimator 220 estimates a channel. Thepost-coder 230 performs post-coding corresponding to the pre-coding ofthe precoders 140-1 to 140-K. The demapper 240 de-maps input symbolsinto coded data. The channel decoder 250 decodes the coded data torestore original data. The controller 260 feeds back feedback data to atransmitter. The feedback data includes channel state information (CSI),channel quality information (CQI), user priority information, etc.

FIG. 4 shows an example of a granularity of a radio resource accordingto an embodiment of the present invention.

Referring to FIG. 4, user data and control signals are carried andtransmitted on a frame including a plurality of resource blocks. Theframe can include a plurality of OFDM symbols in a time axis and aplurality of resource blocks in a frequency axis. The resource block isa basic unit of radio resource allocation, and includes a plurality ofcontiguous subcarriers. The resource block can include 12 subcarriers.The subcarrier includes a data subcarrier and a pilot subcarrier. Thedata subcarrier can carry the user data and the control signals. Thepilot subcarrier can carry common pilots for respective antennas in themultiple antenna system. The subcarrier and the pilot subcarrier can bearranged in various patterns in the resource block.

The radio resource can be divided in the frequency domain into a varietyof granularities, e.g., a whole-band (WB), a PMI-band (PB), a sub-band(SB), etc. The SB denotes a frequency band for carrying at least onecontrol signal or user data. The SB can include at least one resourceblock. The PB includes at least one SB. The PB includes SBs having thesame or similar PMIs. The WB denotes a whole frequency band. A sizerelation of these bands may be SB≦PB≦WB.

According to feedback data reporting, the radio resource can be dividedin the frequency domain into a best band (BB) and a residual band (RB).The BB denotes a set of specific SBs selected from a plurality of SBs.The RB denotes a set of SBs remaining after excluding BBs from the WB.For example, if CQIs are transmitted using a best-M scheme (M=2), twoSBs having greatest CQI values are selected from all SB CQI values. Theselected two SBs are used as BBs, and the remaining SBs are used as RBs.The CQIs of the two BBs may be transmitted without alteration, and theCQIs of the RBs may be transmitted in such as manner that CQIs of allSBs corresponding to the RBs are averaged so that the resultant oneaverage value is transmitted. Alternatively, the CQIs of the two BBs maybe averaged so that the resultant average value is transmitted, and theCQIs of all SBs corresponding to RBs may be averaged so that theresultant average value is transmitted.

The best-M scheme is for selecting a set of specific M SBs from aplurality of SBs. In the best-M scheme, a user equipment (UE) can selecta most preferred SB and report the selected SB to a base station (BS).In the best-M scheme, a CQI of the selected SB can be represented withits original value or may be represented with an average value. A CQI ofthe RB can be represented with an average RB CQI or an average WB CQI.

The aforementioned frame structure and the granularity of the radioresource are provided for exemplary purposes only. Thus, a size of eachband and the number of bands may be variously modified and applied.

The reason of applying a variety of granularities is to reduce anoverhead caused by feedback data and to effectively transmit thefeedback data. For example, to provide a service with good quality ofservice (QoS) to a plurality of UEs, it is effective to obtain andtransmit CQIs for all SBs. However, since transmission of the CQIs ofall SBs results in increase in the overhead, the UE transmits the CQIsin such as manner that, as for BBs, some SBs having good CQIs arespecified as the BBs and their original CQIs are transmitted, whereas,as for RBs, only an average value obtained by averaging the CQIs of theRBs is transmitted.

The PMI is information required for performing preceding and postcodingon user data. The PMI can be obtained with respect to the SB, the PB,and the WB. The CQI is calculated based on the PMI and is thenquantized. For correct CQI reporting, PMIs for all SBs have to betransmitted. However, transmission of the PMIs of all SBs results inincrease in an overhead. An unnecessary overhead can be generatedaccording to a size of the PB even in a case where a PMI for the PB isobtained and transmitted. When the PMI is obtained and transmitted inthe same manner as a CQI transmission method, the unnecessary overheadcan be reduced and correct CQI reporting can be achieved. One CQI andone PMI can be obtained and transmitted for the WB. The PB may have anequal or greater size than the BB. A PMI of the PB belonging to the BBcan be transmitted together with a CQI of the BB.

The RI denotes respective independent channels that can be multiplexedby multiple antennas. The RI can be obtained and transmitted in a WBunit.

Now, a method for transmitting feedback data in a multiple antennasystem will be described.

FIG. 5 shows an example of transmitting a CQI and a PMI. FIG. 6 showsanother example of transmitting a CQI and a PMI. FIG. 7 shows anotherexample of transmitting a CQI and a PMI.

Referring to FIGS. 5 to 7, a whole frequency band is divided into 9 SBs.

In FIG. 5, a CQI's frequency granularity (FG) is determined to be oneSB, and a PMI's FG is determined to be a WB. Feedback data may consistof CQIs of respective SBs and a CQI of the WB.

In FIG. 6, a CQI FG is determined to be one SB, and a PMI FG isdetermined to be greater than the CQI FG. That is, it can be related asPMI FG=N×CQI FG (N>1). The PMI FG may be determined to be a multiple ofthe CQI FG. For example, if two resource blocks are included in the CQIFG, the number of resource blocks included in the PMI FG can be 4, 6, .. . , n, where n is a multiple of 2. Once the PMI FG is determined to bea multiple of the CQI FG, it is easy to calculate a CQI determinedaccording to the PMI. In addition, the PMI can be easily applied.Feedback data may consist of CQIs of all SBs and a PMI of a PMI FG.

In FIG. 7, a CQI FG is determined to be one SB, and a PMI FG is alsodetermined to be one SB. That is, the CQI FG and the PMI FG can bedetermined to have the same size. Feedback data may consist of CQIs andPMIs of all SBs. When the CQI FG and the PMI FG are determined to havethe same size, accuracy of CQI reporting can increase. However, thenumber of PMIs may increase in proportion to the number of transmittedCQIs. Thus, an overhead caused by the feedback data may also increase.

CQIs can be calculated in various manners as follows.

1. A CQI for each SB can be calculated by using a PMI for each SB. ThePMI for each SB is referred to as a frequency selective PMI. The CQI foreach SB is referred to as a frequency selective CQI.

2. The CQI for each SB can be calculated by using a PMI for a WB.

3. The CQI for each SB belonging to an RB can be calculated by using aPMI for the RB remaining after excluding a BB selected according to thebest-M scheme. A PMI for the WB or a PMI for the RB is referred to as afrequency flat PMI.

4. A CQI for each SB belonging to the BB can be calculated by applyingthe frequency selective PMI to the BB selected in the best-M scheme, anda CQI for each SB can be calculated by applying the frequency flat PMIto the SB belonging to the RB.

5. An average CQI for a WB can be calculated in the best-M scheme byusing a CQI value in consideration of a BB. An average CQI for a WB oran RB is referred to as a frequency flat CQI.

6. An average CQI for an RB in the best-M scheme can be calculated byusing a CQI value without consideration of the BB.

7. A BB CQI can be represented with a difference value with respect to aWB CQI in the best-M scheme, and an average CQI can be calculated usingthe RB and the difference value. The CQI average can be used as a CQIaverage for the RB or the WB.

When a CQI applied with the frequency selective PMI is included in CQIcalculation, the average CQI can be increased as a whole. When thenumber of UEs is small, the RB other than the reported BB may also beallocated to the UEs. Since an RB CQI is reported to be a great value, ahigh MCS level can be selected and thus throughput can be improved.

FIG. 8 shows a method for generating feedback data according to anembodiment of the present invention.

Referring to FIG. 8, a WB is divided into a plurality of SBs. A UE canobtain a CQI for each SB. The WB includes 7 SBs. It is assumed hereinthat a 6^(th) SB and a 7^(th) SB are BBs selected from the 7 SBs. Thatis, two SBs having greatest CQI values are selected in the best-M scheme(M=2). The number of the selected SBs is provided for exemplary purposesonly, and thus the present invention is not limited to theaforementioned number.

Feedback data includes various types of control signals. Table 1 belowshows an example of the types of control signals.

TABLE 1 Type bitmap RI CQI PMI A O WB BB #1 CQI BB #1 PMI BB #2 CQI BB#2 PMI RB CQI RB PMI B O WB BB #1 and #2 average BB #1 PMI and BB #2 CQIPMI RB CQI RB PMI A-1 O WB BB #1 CQI BB #1 and #2 PMI BB #2 CQI RB PMIB-1 O WB BB #1 and #2 average BB #1 and #2 PMI CQI RB PMI RB CQI

In Table 1 above, ‘bitmap’ is an indicator for specifying an SB selectedfrom a plurality of SBs. M SBs may be selected and specified with abitmap in the best-M scheme. For example, 7 SBs can be represented witha 7-bit bitmap, and a 6^(th) SB and a 7^(th) SB selected from the 7 SBscan be specified as ‘0000011’. When N BB CQIs selected from N SBs aretransmitted or when a WB CQI is transmitted in the best-M scheme, abitmap may not be transmitted.

‘RI’ is provided for the WB and may be included in the feedback data.

‘CQI’ is provided for each SB selected as a BB and is also provided fora BB or an RB. The CQI may be included in the feedback data.

‘PMI’ is provided for each SB selected as a BB and is also provided fora value for a BB or an RB. The PMI may be included in the feedback data.

It is assumed that ‘CQI’ and ‘PMI’ are included in the feedback datawith the same granularity. In the best-M scheme, the feedback data mayinclude a BB CQI or an RB CQI. The feedback data may include a BB PMI oran RB PMI. The BB CQI may be a CQI for each SB belonging to the BB ormay be one average CQI for BBs. The RB CQI may be an average CQI of SBsbelonging to the RB. The BB PMI may be a PMI of each SB belonging to theBB or may be one PMI for BBs.

In Type ‘A’, a CQI includes a first BB (BB #1) CQI, a second BB (BB #2)CQI, and an RB CQI. A PMI includes a BB #1 PMI, a BB #2 PMI, and an RBPMI.

In Type ‘B’, a CQI includes an average CQI of BB #1 and BB #2 and an RBCQI. A PMI includes a BB #1 PMI, a BB #2 PMI, and an RB PMI.

In Type ‘A-1’, a CQI includes a BB #1 CQI and a BB #2 CQI. A PMIincludes one PMI for both BB #1 and BB #2 and an RB PMI.

In Type ‘B-1’, a CQI includes an average CQI of BB #1 and BB #2 and anRB CQI. A PMI includes one PMI for both BB #1 and BB #2 and an RB PMI.

FIG. 9 shows a method for generating feedback data according to anotherembodiment of the present invention.

Referring to FIG. 9, a WB includes 7 SBs. It is assumed herein that a6^(th) SB and a 7^(th) SB are BBs selected from the 7 SBs. That is, twoSBs having greatest CQIs are selected in the best-M scheme (M=2).

Table 2 below shows an example of various types of feedback data.

TABLE 2 Type Bitmap RI CQI PMI C O WB BB #1 CQI BB #1 PMI BB #2 CQI BB#2 PMI WB CQI WB PMI D O WB BB #1 and #2 average BB #1 PMI and BB #2 CQIPMI WB CQI WB PMI C-1 O WB BB #1 CQI BB #1 and #2 PMI BB #2 CQI WB PMID-1 O WB BB #1 and #2 average BB #1 and #2 PMI CQI WB PMI WB CQI

In the best-M scheme, the feedback data can include a BB CQI and a WBCQI. The feedback data can also include a BB PMI and a WB PMI. The BBCQI may be CQIs of all SBs belonging to the BB or may be one average BBCQI. The WB CQI may be an average WB CQI. The BB PMI may be PMIs of allSBs belonging to the BB or may be one PMI for BBs.

In Type ‘C’, a CQI includes a BB #1 CQI, a BB #2 CQI, and a WB CQI. APMI includes a BB #1 PMI, a BB #2 PMI, and a WB PMI.

In Type ‘D’, a CQI includes an average CQI of BB #1 and BB #2 CQI and aWB CQI. A PMI includes a BB #1 PMI, a BB #2 PMI, and a WB PMI.

In Type ‘C-1’, a CQI includes a BB #1 CQI and a BB #2 CQI. A PMIincludes one PMI for BBs #1 and #2 and a WB PMI.

In Type ‘D-1’, a CQI includes an average CQI of BB #1 and BB #1 and a WBCQI. A PMI includes one PMI for BBs #1 and #2 and a WB PMI. A userequipment (UE) selects M SBs from a plurality of SBs, and reports to abase station (BS) one PMI and one CQI for the selected SBs (i.e., BBs).Herein, one PMI for the selected M SBs indicates an index of onepreceding matrix selected from a codebook set used when transmission ismade through the selected M SBs. One CQI for the selected M SBs uses thepreceding matrix used in the selected M SBs. A difference value withrespect to the WB CQI can be used as a CQI value for the selected M SBs.The UE reports to the BS a WB PMI and a WB CQI for a WB including aplurality of SBs. The WB PMI indicates an index of a preceding matrixselected from a codebook for all of the plurality of SBs. The WB CQIindicates a CQI value for all of the plurality of SBs.

The types of control signals described in Table 1 and Table 2 above canbe used in combination with each other. For example, CQIs transmittedthrough the feedback data may be the average BB CQI and the WB CQI, andPMIs transmitted through the feedback data may be the BB PMI and the RBPMI.

A scheme for transmitting the WB PMI or the RB PMI is referred to as aPMI compression scheme.

As described above, when a CQI is obtained for an SB in transmission, aPMI is obtained for the same SB and is then transmitted. In addition,when one CQI is obtained for an RB or a WB in transmission, one PMI isobtained for the RB and the WB and is then transmitted. The UE transmitsthe CQI and the PMI by using the same granularity value, therebyreducing an overhead caused by feedback data.

The aforementioned description is for exemplary purposes only, and thusthe present invention is not limited thereto. For example, only a BB CQImay be transmitted without transmitting a WB CQI or an RB CQI, and as aresult, only a BB PMI may be transmitted.

Table 3 blow shows another example of various types of feedback data.This is a case where only an SB CQI and an SB PMI are transmitted.

TABLE 3 Type Bitmap RI CQI PMI E O WB BB #1 CQI All of SB PMI/ BB #2 CQIWB PMI F O WB BB #1 CQI BB #1 PMI BB #2 CQI BB #2 PMI G O WB BB #1 CQIBB #1 and #2 PMI BB #2 CQI BB #1 and #2 PMI H O WB BB #1 and #2 averageCQI

In Type ‘E’, a CQI includes a BB #1 CQI and a BB #2 CQI. A PMI includesall of each SB PMIs or a WB PMI.

In Type ‘F’, a CQI includes a BB #1 CQI and a BB #2 CQI. A PMI includesa BB #1 PMI and a BB #2 PMI.

In Type ‘G’, a CQI includes a BB #1 CQI and a BB #2 CQI. A PMI includesone PMI for both BB #1 and BB #2.

In Type ‘H’, a CQI includes an average CQI for both BB #1 and BB #2. APMI includes one PMI for both BB #1 and BB #2.

Table 4 below shows another example of various types of feedback data.This is a case where only a WB CQI and a WB PMI are transmitted.

TABLE 4 Type Bitmap RI CQI PMI I x WB WB CQI WB PMI J x x WB CQI WB PMI

Since the WB CQI and the WB PMI are transmitted, bitmap information isnot required.

In Type ‘I’, a CQI is a WB CQI, and a PMI is a WB PMI. In Type ‘J’, rankinformation is not given. A CQI is a WB CQI, and a PMI is a WB PMI.

A granularity of a PMI-band (PB) can be determined variously accordingto a type of feedback data.

A PB may have the same granularity as an SB or may have a granularitygreater than the SB and less than a WB. The PB may be variable. Thegranularity of the PB can be determined as follows.

(1) Smallest PMI Band (S-PB)

The PB has the same granularity as the SB (i.e., PB=SB): (a) Thegranularity of the PB can be determined to be the same granularity asSBs for M CQIs.

(2) Middle PMI Band; (M-PB)

The PB has a granularity greater by an integer multiple number than theSB (i.e., SB<PB<WB): (a) The granularity of the PB can be determined tohave the size of contiguous SBs for M CQIs; (b) When M average CQIs aretransmitted, M SBs can be determined as the PB; and (c) (N-M) SBs whichare non-selected bands among N SBs can be determined as the PB.

(3) Largest PMI Band (L-PB)

The PB has the same granularity as the WB (i.e., PB=WB): (a) Thegranularity of the PB can be determined to have the same granularity asthe WB.

Now, a granularity of a PB according to a reporting type of feedbackdata will be described.

If the reporting type of feedback data is ‘A’ or ‘B’ of Table 1 above,the granularity of the PB for an SB CQI can be S-PB, M-PB(a), orM-PB(b). The granularity of the PB for an RB CQI can be M-PB(c).

If the reporting type of feedback data is ‘C’ or ‘D’ of Table 2 above,the granularity of the PB for the SB CQI can be S-PB, M-PB (a), or M-PB(b). The granularity of the PB for a WB CQI can be M-PB(c) or L-PB. Inaddition, when the number M of selected bands is equal to the number Nof all SBs, the granularity of the PB for the SB CQI can be S-PB, andthe granularity of the PB for an average WB CQI can be L-PB.

If the reporting type of feedback data is ‘E’, ‘F’, ‘G’, or ‘H’ of Table3 above, the granularity of the PB for the SB CQI can be S-PB, M-PB(a),or M-PB(b). Further, the granularity of the PB for the WB can be M-PB(c)or L-PB.

If the reporting type of feedback data is ‘I’ or ‘J’ of Table 4 above,the granularity of the PB for the WB CQI can be L-PB.

FIGS. 10 to 12 show a method for transmitting feedback data according toan embodiment of the present invention. More specifically, FIG. 10 showsa case of transmitting a WB PMI, FIG. 11 shows a case of transmitting aPMI for a PMI FG having a greater size than a CQI FG, and FIG. 12 showsa case of transmitting a PMI for a PMI FG having the same size as theCQI FG.

Referring to FIGS. 10 to 12, an uplink overhead can be reduced when onePMI is transmitted for a WB. In this case, a CQI to be transmitted mayinclude a BB (i.e., BB #1 and BB #2) CQI and a WB CQI or may include aBB CQI and an RB CQI.

When the PMI FG has a size two times higher than the CQI FG, one PMI(i.e., PMI #A) may be transmitted for the BBs #1 and #2 having greatestCQI levels, and two PMIs (i.e., PMIs #C and #F) may be transmitted forRBs #3 to #5. Although the WB PMI is transmitted in this case, theuplink overhead can be reduced when the PMI FG is determined to have agreater size than the CQI FG. When the PMI is represented in 4 bits,resources of 12 bits are used to transmit the PMI. In this case, a CQIto be transmitted may include a BB (i.e., BB #1 and BB #2) CQI and a WBCQI or may include a BB CQI and an RB CQI.

When the PMI FG and the CQI FG have the same size, the PMI #A and thePMI #B of the respective BBs #1 and #2 and the PMI #C and the PMI #F ofthe respective RBs #3 and #5 can be transmitted. Although datathroughput can increase in this case, the uplink overhead maysignificantly increase. When the PMI is represented in 4 bits, resourcesof 24 bits are used to transmit 6 PMIs. In this case, a CQI to betransmitted may include a BB (i.e., BB #1 and BB #2) CQI and a WB CQI ormay include a BB CQI and an RB CQI.

The aforementioned number of SBs and BBs for generating feedback datacan vary variously. The size and the number of PBs also can varyvariously. PMIs can be transmitted in various manners. For example, a BBPMI and a WB PMI can be transmitted, or only PMIs for some BBs selectedfrom a plurality of BBs can be transmitted.

Now, a method for transmitting PMIs of some SBs (i.e., BBs) instead oftransmitting all PMIs of a whole frequency band will be described.

FIGS. 13 and 14 show a method for transmitting feedback data accordingto another embodiment of the present invention. This is a case where aPMI FG is greater in size than a CQI FG (i.e., PMI FG=N×CQI FG (N>1)).

Referring to FIGS. 13 and 14, a PMI of a BB having a high CQI istransmitted, and a PMI of an RB is additionally transmitted whennecessary. This is referred to as a BB PMI scheme. PMIs of respectivePBs belonging to the BB are transmitted, and then an RB PMI or a WB PMIcan be transmitted. The number of PMIs to be transmitted by a UE may bedetermined according to the number of BBs and a ratio of a CQI FG to aPMI FG.

It is assumed that the PMI FG has a size two times higher than the CQIFG, and two SBs are selected as BBs (i.e., M=2). In FIG. 13, theselected BBs are included in one PMI FG. The number of PMIs to betransmitted by the UE is one. In FIG. 14, the selected two BBs areincluded in different PMI FGs. The number of PMIs to be transmitted bythe UE is two. The UE may transmit a WB PMI(2) along with a PMI(1) of aPB belonging to the BB, or may transmit an RB PMI(3).

FIGS. 15 and 16 show a method for transmitting feedback data accordingto another embodiment of the present invention. This is a case where aPMI FG and a CQI FG have the same size.

Referring to FIGS. 15 and 16, when the PMI FG and the CQI FG have thesame size, one PMI is assigned for one CQI. When the CQI and the PMI arereported in the best-M scheme, the CQI and the PMI can be reported withone bitmap. A UE may transmit a WB PMI(2) together with a BB PMI(1) ormay transmit an RB PMI(3).

When the BB PMI is transmitted together with the WB (or RB) PMI, a bandapplied with each PMI can be known by using the reported CQI. Forexample, when the UE reports a BB CQI by selecting M BBs, the UE canreport the BB PMI together with the BB CQI. In this case, an indexindicating a BB in CQI reporting can also be used without alternation inPMI reporting.

Even when applying the PMI FG and the CQI FG having different sizes, aband applied with a PMI reported through the index indicating the BB canbe known. The UE may report control signals, for example, CQI₁, . . . ,CQI_(M), CQI_(Average), BitMap, PMI₁, . . . , PMI_(L), and PMI_(Average)(M>L). When an average PMI (i.e., PMI_(Average)) is located in a lastposition of a reported area, information on remaining PMIs other thanthe average PMI is sequentially used as information on BB PMIs.

Herein, “CQI₁, . . . , CQI_(M), CQI_(Average), BitMap” is an expressionin consideration of CQI compression of the best-M scheme. A PMIcompression scheme can be used along with any CQI compression schemes.For example, if the UE compresses CQI information of each SB by usingdiscrete cosine transform (DCT) and transmits the compressed CQIinformation, the BS can know each SB CQI according to compressioninformation. Accordingly, a position of a BB can be known, and theposition of the BB is a position applied with a BB PMI.

FIGS. 17 to 20 show a method for transmitting feedback data according toanother embodiment of the present invention. This is a case where a PMIFG has a size two times higher than a CQI FG, and two BBs having goodCQIs are selected (i.e., M=2).

Referring to FIGS. 17 to 20, in FIG. 17, when BBs #1 and #2 are includedin one PMI FG, a UE transmits one PMI #A for the BBs #1 and #2 and a PMI#G for a WB. In this case, the UE may transmit CQIs of the BBs #1 and #2and an average WB CQI.

In FIG. 18, when the BBs #1 and #2 are included in one PMI FG, the UEtransmits one PMI #A for the BBs #1 and #2 and a PMI #H for an RB. Inthis case, the UE may transmit CQIs of the BBs #1 and #2 and an RB CQI.

In FIG. 19, when the BBs #1 and #3 are included in different PMI FGs,the UE transmits PMIs #A and #C for the respective PMI FGs and a PMI #Gfor a WB. In this case, the UE may transmit CQIs of the BBs #1 and #3and an average WB CQI.

In FIG. 20, when the BBs #1 and #3 are included in different PMI FGs,the UE transmits PMIs #A and #C for the respective PMI FGs and a PMI #Gfor an RB. In this case, the UE may transmit CQIs of the BBs #1 and #3and an RB CQI.

FIGS. 21 to 24 show a method for transmitting feedback data according toanother embodiment of the present invention. This is a case where a PMIFG and a CQI FG have the same size, and two BBs having high CQIs areselected (i.e., M=2).

Referring to FIGS. 21 to 24, in FIG. 21, a UE transmits PMIs #A and #Bfor respective BBs #1 and #2 and a PMI #G for a WB. In this case, the UEmay transmit CQIs of the BBs #1 and #2 and an average WB CQI.

In FIG. 22, the UE transmits PMIs #A and #B for respective BBs #1 and #2and a PMI #H for an RB. In this case, the UE may transmit CQIs of theBBs #1 and #2 and an RB CQI.

In FIG. 23, the PMI FG and the CQI FG have the same size even ifselected BBs are not contiguous to each other. Thus, the UE can transmitPMIs #A and #C for respective BBs #1 and #3 and a PMI #H for an RB. Inthis case, the UE may transmit CQIs of the BBs #1 and #3 and an RB CQI.

In FIG. 24, even if selected BBs are not contiguous to each other, theUE can transmit PMIs #A and #C for respective BBs #1 and #3 and a PMI #Gfor a WB. In this case, the UE may transmit CQIs of the BBs #1 and #3and a WB CQI.

When a BB PMI and a WB PMI are transmitted or when a BB PMI and an RBPMI are transmitted, the following gain can be obtained.

1. If a CQI FG and a PMI FG have the same size, a granularity applied toa PMI is the same as that applied to a CQI. Thus, the PMI and the CQIcan be easily mapped.

2. If the CQI FG and the PMI FG have different sizes, the following isapplied. (1) The PMI and the CQI can be more easily mapped when the PMIFG and the CQI FG have a multiple relation than when the PMI FG and theCQI FG have a relatively prime relation. (2) It is easy to use a PMIcompression scheme together with a CQI compression scheme when the PMIFG has a larger size than the CQI FG and has a multiple relation to theCQI FG. That is, a BB PMI transmission method and a BB CQI transmissionmethod can be easily used. (3) When some of PMIs are to be transmitted,there is a need to inform which SB PMIs are transmitted. For example,selected SBs may be informed using a bitmap. Alternatively, in case of aPMI for an SB applied with a best-M CQI, the PMI can be used bysearching for information indicating a position of a BB CQI.

FIGS. 25 to 27 show a method for transmitting feedback data according toanother embodiment of the present invention.

Referring to FIGS. 25 to 27, a CQI and a PMI can be transmitted byconfiguring a PMI FG to have a larger size than a CQI FG and byselecting contiguous BBs included in one PMI FG.

To allow the contiguous BBs to be included in one PMI FG, the followingis carried out. (1) A PMI-band (PB) including an SB having a goodchannel condition is obtained. The PMI-band includes at least one SB andat least one CQI-band. (2) M BBs are selected from the obtainedPMI-band. The BB is a CQI-band including at least one SB. (3) CQIs ofthe BBs selected from one PMI FG are obtained. (4) A BB CQI and a WB (orRB) CQI are transmitted. (5) A PMI of a PMI-band including the BBs and aPMI of a WB (or RB) are transmitted. The number of transmitted PMIs isdetermined according to a value M given in the best-M scheme. The numberof reporting PMIs can be determined according to the value M as follows.

No. of reporting PMI=┌M/N┐

Herein, N=PMI FG/CQI FG. The PMI FG can be determined to be a multipleof the CQI FG. That is, the number of SBs belonging to the PMI-band is amultiple of the number of SBs included in the BB (i.e., CQI-band). M maybe a default value or may be determined by a BS and reported to a UE.When the number of reporting PMIs is determined according to thedetermined M, feedback data reported by the UE to the BS can bedetermined in a specific format. In addition, a bitmap indicating the BBcan be reused as a bitmap indicating the PMI-band. When the feedbackdata transmitted by the UE is determined to the specific format, the BScan avoid a complex process such as blind decoding, thereby increasingsystem efficiency.

In FIG. 25, PMIs #A and #B of a PMI FG corresponding to randomlyselected BBs and a PMI #C of an RB are transmitted. CQIs to betransmitted include a BB CQI and a WB CQI. The WB CQI may be an averageCQI for a plurality of BBs. Instead of the WB CQI, an RB CQI may betransmitted. There is no particular overhead reduction.

In FIG. 26, when contiguous BBs are selected and the selected BBs areincluded in one PMI FG, one PMI #A for the BBs and PMIs #B and #C forRBs can be transmitted. When only the PMIs for the BBs are transmitted,an overhead can be reduced.

In FIG. 27, when contiguous BBs are selected and the selected BBs areincluded in one PMI FG, one PMI #A for the BBs and a PMI #D for an RBcan be transmitted. An overhead caused by PMI transmission can befurther reduced. As such, when feedback data is transmitted byconfiguring the PMI FG to be larger than the CQI FG and by selectingcontiguous BBs included in one PMI FG, an overhead caused by feedbackdata transmission can be reduced.

FIG. 28 is a graph showing an example of a data efficiency ratio when anuplink PMI is transmitted. FIG. 29 is a graph showing another example ofa data efficiency ratio when an uplink PMI is transmitted. Four BBs areselected in FIG. 28 (i.e., M=4 in the best-M scheme). Six BBs areselected in FIG. 29 (i.e., M=6 in the best-M scheme).

Referring to FIGS. 28 and 29, “(a) Scheme 1” is a case where a PMI istransmitted as shown in FIG. 25. “(b) Scheme 2” is a case where a PMI istransmitted as shown in FIG. 26. “(c) Scheme 3” is a case where a PMI istransmitted as shown in FIG. 27.

In “Scheme 3”, one PMI is transmitted by selecting contiguous BBs andthen an RB PMI is transmitted (i.e., a PMI compression scheme). In termsof data efficiency, the use of this scheme shows almost the same resultas in a case of transmitting all PMIs. That it, an overhead caused bycontrol signal transmission can be reduced while maintaining systemperformance.

FIG. 30 is a flowchart showing a method for generating feedback dataaccording to an embodiment of the present invention.

Referring to FIG. 30, a BS requests a UE to report feedback data througha downlink channel (step S110). The feedback data report request can betransmitted using a request message. The request message may includeuplink scheduling information for channel condition reporting and alsoinclude information on a frame offset, a reporting type of the feedbackdata, a transmission period of the feedback data, etc. The uplinkscheduling information indicates feedback data transmission and uplinkradio resource assignment. The request message may be transmittedthrough a physical downlink control channel (PDCCH).

The UE generates the feedback data (step S120). The UE extracts channelinformation from a downlink signal. The channel information may includechannel state information (CSI), channel quality information (CQI), userpriority information, etc. By using the channel information, the UEselects M SBs from a plurality of SBs according to a channel conditionbetween the UE and the BS. The M SBs may be selected from the pluralityof SBs according to a CQI value of each SB. The UE generates thefeedback data according to a reporting type of the feedback data. Thereporting type may be determined by the BS or may be predetermined bydefault. For example, the feedback data may include a frequencyselective PMI, a frequency flat PMI, a BB CQI, and a WB CQI. Thefeedback data may further include a bitmap and an RI. The bitmapindicates positions of the selected M SBs. The RI corresponds to thenumber of useful transmission layers. The BB CQI and the WB CQI may becalculated for each transmission layer. A CQI reporting type may varyaccording to each layer.

The UE reports the feedback data to the BS through an uplink channel(step S130). The UE transmits the feedback data by using an uplink radioresource allocated according to uplink scheduling information. Theuplink radio resource may be a physical uplink shared channel (PUSCH).

The BS performs radio resource scheduling by using the feedback datareceived from the UE. Errors may occur in the feedback data in theprocess of transmitting the feedback data. The feedback data transmittedby the UE may not be correctly decoded by the BS, and in this case, thefrequency selective PMI cannot be used. Regarding a PMI included in thefeedback data, the UE selects a PMI which can be best fit to its channelcondition. In terms of improvement of quality of service (QoS), it ispreferable that the BS allocates radio resources by using the PMIincluded in the feedback data.

FIG. 31 is a flowchart showing a method for selecting a PMI by detectingan error from feedback data according to an embodiment of the presentinvention. It is assumed herein that a UE transmits feedback data to aBS by using the best-M scheme, wherein the feedback data includes an SBPMI and a WB PMI (or RB PMI).

Referring to FIG. 31, the BS receives the feedback data from the UE(step S210). The feedback data may include a bitmap indicating a BBselected according to the best-M scheme, a PMI of an SB belonging to theBB, and a PMI of an RB (or a WB).

The BS detects an error of the bitmap from the feedback data transmittedby the UE (step S220). Due to noise or fading, the feedback data may notbe correctly decoded when it is transmitted from the UE to the BS.

If there is no error in the bitmap, the BS applies the SB PMItransmitted by the UE (step S230). That is, the BS assigns to the UE atleast one SB selected by the UE from the BBs. In addition, for a PMI ofthe assigned SB, the BS applies the SB PMI transmitted by the UE.

Otherwise, if there is an error in the bitmap, the BS applies the WB PMIor the RB PMI (step S240). Since the BS cannot know the BBs due to thebitmap error, the BS cannot use the SB PMI transmitted by the UE. The BSallocates radio resources to the UE according to the WB PMI or the RBPMI transmitted by the UE. The BS reports to the UE a PMI currently inuse together with radio resource assignment information by using adownlink control signal.

Since the BS can adaptively select a PMI to be used in radio resourcesaccording to a result of detecting errors from feedback data, QoS ofwireless communication can be improved.

An overhead caused by transmission of feedback data can be reduced, andradio resource scheduling can be effectively achieved in a multipleantenna system.

Every function as described above can be performed by a processor suchas a microprocessor based on software coded to perform such function, aprogram code, etc., a controller, a micro-controller, an ASIC(Application Specific Integrated Circuit), or the like. Planning,developing and implementing such codes may be obvious for the skilledperson in the art based on the description of the present invention.

Although the embodiments of the present invention have been disclosedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope of the invention. Accordingly, the embodimentsof the present invention are not limited to the above-describedembodiments but are defined by the claims which follow, along with theirfull scope of equivalents.

1. A method of transmitting feedback data in a multiple antenna system,the method comprising: receiving a request message of feedback data on adownlink channel, the request message comprising uplink schedulinginformation; selecting a set of M (M≧1) subbands within a plurality ofsubbands; generating the feedback data, the feedback data comprising afrequency selective PMI (preceding matrix indicator), a frequency flatPMI, a best band CQI (channel quality indicator) and a whole band CQI,the frequency selective PMI indicating the index of a preceding matrixselected from a codebook over the M selected subbands, the frequencyflat PMI indicating the index of a preceding matrix selected from thecodebook over the plurality of subbands, the best band CQI indicating aCQI value over the M selected subbands, the whole band CQI indicating aCQI value over the plurality of subbands; and transmitting the feedbackdata on a uplink channel allocated to the uplink scheduling information.2. The method of claim 1, wherein the feedback data further comprises arank indicator (RI), the RI corresponding to the number of usefultransmission layers, and the best band CQI and the whole band CQI arecalculated for each transmission layer.
 3. The method of claim 1,wherein the feedback data further comprises a bitmap which representsthe positions of the M selected subbands.
 4. The method of claim 1,wherein the downlink channel is a physical downlink control channel(PDCCH).
 5. The method of claim 1, wherein the uplink channel is aphysical uplink shared channel (PUSCH).
 6. The method of claim 1,wherein the best band CQI has a differential CQI value with respect tothe whole band CQI.
 7. The method of claim 1, wherein the uplinkscheduling information comprises an indicator indicating transmission ofthe feedback data and uplink radio resource assignment.
 8. The method ofclaim 1, wherein the set of M subbands is selected within the pluralityof subbands according to a CQI for each subband.
 9. A method oftransmitting feedback data in a multiple antenna system, the methodcomprising: selecting a set of M (M≧1) subbands within a plurality ofsubbands; and transmitting feedback data on a uplink shared channel, thefeedback data comprising a frequency selective PMI, a frequency flatPMI, a best band CQI and a whole band CQI, the frequency selective PMIindicating the index of a preceding matrix selected from a codebook overthe M selected subbands, the frequency flat PMI indicating the index ofa preceding matrix selected from the codebook over the plurality ofsubbands, the best band CQI indicating a CQI value over the M selectedsubbands, the whole band CQI indicating a CQI value over the pluralityof subbands.
 10. The method of claim 9, further comprising: receiving arequest message of feedback data on a downlink control channel, therequest message comprising uplink scheduling information, wherein theuplink shared channel is transmitted by using the uplink schedulinginformation.
 11. The method of claim 9, wherein the feedback datafurther comprises a RI over the plurality of subbands.
 12. The method ofclaim 9, wherein the feedback data further comprises a bitmap whichrepresents the positions of the M selected subbands.
 13. The method ofclaim 9, wherein the best band CQI has a differential CQI value withrespect to the whole band CQI.